The present invention relates in general to a method and apparatus for the control of the dispatch of elevator cars from a main floor and, in particular, to such control during up peak traffic conditions.
A dispatch control for an elevator group consisting of several elevators is shown in the European Pat. No. 0 030 163, in which the dispatch interval is based on an approximate round trip time (RTT) of an elevator car, or on a mean round trip time based on the three preceding, approximate round trip times. The round trip time is divided by the number of elevator cars serving the main floor to determine a mean dispatch time interval. The approximate round trip time is the expected time which the elevator car requires for the up trip, serving the car calls registered at the main floor and the return trip to the main floor, and is calculated from building parameters, elevator installation parameters and operating condition parameters. If the elevator car has reached less than half its nominal load after expiration of the calculated dispatch interval time, the calculated interval time for the cars available at the main floor is shortened. If the elevator car reaches, after expiration of the calculated dispatch time interval, at least half its nominal load, the interval time is shortened in a similar manner, however, with different weighting of the available cars.
A disadvantage of the above described control is that the actual dispatching time interval is determined on the basis of approximate round trip times calculated from past data. This permits, in the best case, an estimate of the dispatching interval necessary for serving the actual traffic requirements. A further drawback is the fact that the control distinguishes only between a departure load being smaller than half the nominal load, and a departure load which is at least equal to half the nominal load, and in doing so shortens the interval time based on the number of cars available at the main floor. There results again only an approximate matching with the effective variations of the traffic requirements. A consequence of both drawbacks is that the utilization of the elevator cars is not optimized.